Why does indexing a DispatchedTuple always return a tuple?

[ali-ramadhan]

I noticed that indexing a DispatchedTuple always returns a tuple:

julia> dispatch(dt, Center())
("c",)

which I thought might introduce lots of [1] boilerplate if I used it since I usually want the contents of the 1-tuple

julia> dispatch(dt, Center())[1]
"c"

but maybe this is because I'm focusing on the case where each object maps to just one value.

Is it always returning a tuple because you want the type of the output to always be <:Tuple? I guess returning [1] in the case of a 1-tuple might introduce type instability?

[charleskawczynski]

Is it always returning a tuple because you want the type of the output to always be <:Tuple?

I think so, yes. DispatchedSets return the value:

using DispatchedTuples
struct Foo end;
struct Bar end;
struct Baz end;

tup = (
   Pair(Foo(), 1),
   Pair(Bar(), 3),
)

dtup = DispatchedSet(tup);

dispatch(dtup, Foo()) # returns 1
dispatch(dtup, Bar()) # returns 3
dispatch(dtup, Baz()) # error

dtup = DispatchedSet(tup, 0);

dispatch(dtup, Foo()) # returns 1
dispatch(dtup, Bar()) # returns 3
dispatch(dtup, Baz()) # returns 0

[charleskawczynski]

I guess returning [1] in the case of a 1-tuple might introduce type instability?

Yeah, probably

[ali-ramadhan]

Ah thanks for the clarification. Indeed DispatchedSet is probably what I want in this case.

I guess this suggests that you want to be iterating over the result of indexing a DispatchedTuple, e.g.

for v in dt[Face()]
    # do something with v...
end

which will always do the right thing.

[charleskawczynski]

I guess this suggests that you want to be iterating over the result of indexing a DispatchedTuple,

Yes, exactly